The least understood process of the inner ear, the transduction of mechanical stimuli into electrical responses, is also the stage at which severe pathology of the auditory and vestibular systems most often arises. We propose to employ the techniques of cell biology and membrane biophysics to investigate how transduction normally operates and how it is affected by a clinically important class of ototoxic agents, the aminoglycoside antibiotics. These studies will contribute to an understanding of transduction which, in the long term, will aid in the rational design of prophylaxis or treatment for conditions such as aminoglycoside ototoxicity, acoustic trauma, presbyacusis, and Meniere's disease. Hair cells from the bullfrog's inner ear will be maintained in vitro either within the saccular epithelium or as solitary cells dissociated by enzymes. The relationship between deflection of a cell's mechanosensitive hair bundle and the resultant receptor potential and membrane conductance changes will be carefully studied with stimuli of a variety of frequencies, amplitudes, and waveforms. The results will be of value in modeling the operation of less accessible organs such as the mammalian cochlea and vestibular apparatus. The subcellular site at which transduction occurs will be sought both by measuring the pattern of current flow around the hair bundle and by localizing the influx of calcium ion through activated transduction channels. The permeability of the transducer's ionic channel will be plumbed with radioactive tris(hydroxymethyl) aminomethane, an ion whose intracellular accumulation may also serve to label stimulated hair cells. As a step toward elucidation of the mechanism whereby aminoglycoside antibiotics damage hair cells, the site of action and binding kinetics of these drugs will be determined. It should be possible to learn whether ototoxic antibiotics interfere with cellular metabolism or exert their effects upon binding to a membrane receptor. Voltage-clamp experiments will be performed on isolated hair cells in order to estimate the conductance of individual transduction channels and to identify other membrane conductance mechanisms that affect the form of the receptor potential.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS020429-03
Application #
3400764
Study Section
Communication Sciences and Disorders (CMS)
Project Start
1983-07-01
Project End
1987-04-30
Budget Start
1985-05-01
Budget End
1986-04-30
Support Year
3
Fiscal Year
1985
Total Cost
Indirect Cost
Name
University of California San Francisco
Department
Type
Schools of Medicine
DUNS #
073133571
City
San Francisco
State
CA
Country
United States
Zip Code
94143
Ghosh, P; Stroud, R M (1991) Ion channels formed by a highly charged peptide. Biochemistry 30:3551-7
Hudspeth, A J (1989) Mechanoelectrical transduction by hair cells of the bullfrog's sacculus. Prog Brain Res 80:129-35;discussion 127-8
Denk, W; Webb, W W; Hudspeth, A J (1989) Mechanical properties of sensory hair bundles are reflected in their Brownian motion measured with a laser differential interferometer. Proc Natl Acad Sci U S A 86:5371-5
Kroese, A B; Das, A; Hudspeth, A J (1989) Blockage of the transduction channels of hair cells in the bullfrog's sacculus by aminoglycoside antibiotics. Hear Res 37:203-17
Howard, J; Hudspeth, A J (1988) Compliance of the hair bundle associated with gating of mechanoelectrical transduction channels in the bullfrog's saccular hair cell. Neuron 1:189-99
Howard, J; Roberts, W M; Hudspeth, A J (1988) Mechanoelectrical transduction by hair cells. Annu Rev Biophys Biophys Chem 17:99-124
Roberts, W M; Howard, J; Hudspeth, A J (1988) Hair cells: transduction, tuning, and transmission in the inner ear. Annu Rev Cell Biol 4:63-92
Howard, J; Hudspeth, A J (1987) Mechanical relaxation of the hair bundle mediates adaptation in mechanoelectrical transduction by the bullfrog's saccular hair cell. Proc Natl Acad Sci U S A 84:3064-8
Eatock, R A; Corey, D P; Hudspeth, A J (1987) Adaptation of mechanoelectrical transduction in hair cells of the bullfrog's sacculus. J Neurosci 7:2821-36
Holton, T; Hudspeth, A J (1986) The transduction channel of hair cells from the bull-frog characterized by noise analysis. J Physiol 375:195-227

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